Repeater for receiving signals from a base station in a wireless communication system, and signal receiving method

ABSTRACT

Disclosed are a repeater for receiving signals from a base station in a wireless communication system, and a signal receiving method. The base station reports, to each repeater, information on the aggregation level of a relay-control channel element (R-CCE) of a relay-physical downlink control channel (R-PDCCH) via an explicit signaling method or implicit signaling method. In the event the base station reports via an explicit signaling method, the repeater receives, from the base station, information on the aggregation level of R-CCE which is a transmission unit of R-PDCCH, wherein the information contains control information for the repeater. Then, the repeater decodes an R-PDCCH region on an R-CCE aggregation level basis in accordance with the received R-CCE aggregation level information.

TECHNICAL FIELD

The present invention relates to wireless communication, and moreparticularly, to a relay node for receiving signals and a signalreception method of the relay node.

BACKGROUND ART

As an example of a mobile communication system to which the presentinvention is applicable, a 3rd Generation Partnership Project Long TermEvolution (hereinafter, “LTE”) and LTE-Advanced (hereinafter, “LTE-A”)communication system is described in brief.

FIG. 1 is a diagram schematically showing a network structure of anE-UMTS as an exemplary mobile communication system.

Referring to FIG. 1, an Evolved Universal Mobile TelecommunicationsSystem (E-UMTS) is an advanced version of a conventional UniversalMobile Telecommunications System (UMTS) and basic standardizationthereof is currently underway in the 3GPP. E-UMTS may be generallyreferred to as a Long Term Evolution (LTE) system. For details of thetechnical specifications of the UMTS and E-UMTS, reference can be madeto Release 7 and Release 8 of “3rd Generation Partnership Project;Technical Specification Group Radio Access Network”.

Referring to FIG. 1, the E-UMTS includes a User Equipment (UE), eNode Bs(eNBs), and an Access Gateway (AG) which is located at an end of thenetwork (E-UTRAN) and connected to an external network. The eNBs maysimultaneously transmit multiple data streams for a broadcast service, amulticast service, and/or a unicast service.

One or more cells may exist in one eNB. A cell is set to use one ofbandwidths of 1.25, 2.5, 5, 10, and 20 MHz to provide a downlink oruplink transport service to several UEs. Different cells may be set toprovide different bandwidths. The eNB controls data transmission andreception for a plurality of UEs. The eNB transmits downlink schedulinginformation with respect to downlink data to notify a corresponding UEof a time/frequency domain in which data is to be transmitted, coding,data size, and Hybrid Automatic Repeat and reQuest (HARQ)-relatedinformation. In addition, the eNB transmits uplink schedulinginformation with respect to uplink data to a corresponding UE to informthe UE of an available time/frequency domain, coding, data size, andHARQ-related information. An interface for transmitting user traffic orcontrol traffic may be used between eNBs. A Core Network (CN) mayinclude the AG, a network node for user registration of the UE, and thelike. The AG manages mobility of a UE on a Tracking Area (TA) basis,wherein one TA includes a plurality of cells.

Although radio communication technology has been developed up to LTEbased on Wideband Code Division Multiple Access (WCDMA), demands andexpectations of users and providers continue to increase. In addition,since other radio access technologies continue to be developed, newtechnical evolution is required to secure future competitiveness.Decrease of cost per bit, increase of service availability, flexible useof a frequency band, simple structure, open interface, and suitablepower consumption by a UE are required.

Recently, 3GPP has been establishing a standard task for a subsequenttechnique of LTE. In this specification, such a technique is referred toas “LTE-A”. One of the main differences between an LTE system and anLTE-A system is system bandwidth and the introduction of a Relay Node(RN). The LTE-A system is aimed at supporting a broadband of a maximumof 100 MHz and, to this end, the LTE-A system is designed to use acarrier aggregation or bandwidth aggregation technique using a pluralityof frequency blocks. Carrier aggregation employs a plurality offrequency blocks as one large logical frequency band in order to use awider frequency band. A bandwidth of each frequency block may be definedbased on a bandwidth of a system block used in the LTE system. Eachfrequency block is transmitted using a component carrier.

As described above, in the LTE-A system introducing the RN, researchinto resource allocation for transmitting control information for the RNand resource allocation for transmitting system information (orbroadcast information) for the RN has not been conducted. In addition, aspecific method in which an eNB signals control information for the RNand resource allocation information for broadcast informationtransmission has not been proposed.

Furthermore, although it is necessary to know a start point of anR-PDSCH in order for the RN to perform decoding by successfullyreceiving signals and control information from the eNB, a specificmethod therefor has not been proposed.

DETAILED DESCRIPTION OF THE INVENTION Technical Problems

It is a technical object of the present invention to provide a methodfor receiving signals at an RN in a wireless communication system.

It is another technical object of the present invention to provide an RNfor receiving signals in a wireless communication system.

It will be appreciated by persons skilled in the art that that thetechnical objects to be achieved by the present invention are notlimited to what has been particularly described hereinabove and othertechnical objects not mentioned above will be more clearly understoodfrom the following detailed description.

Technical Solutions

To achieve the above technical object, a method for receiving signals ata relay node (RN) in a wireless communication system includes receivinginformation about an aggregation level of a Relay-Control ChannelElement (R-CCE) from an eNode B, wherein the R-CCE is a transmissionunit of a Relay-Physical Downlink Control Channel (R-PDCCH) includingcontrol information for the relay node, and decoding the R-PDCCH inunits of the R-CCE aggregation level based on the received informationabout the R-CCE aggregation level.

The method may further include receiving a signal from the eNode Bthrough a Relay-Physical Downlink Shared Channel (R-PDSCH) correspondingto the R-PDCCH based on control information of the decoded R-PDCCH.

The R-CCE aggregation level may be any one of 1, 2, 4, and 8 and may beapplied to each of specific control information. The R-CCE aggregationlevel may be transmitted through a specific field of an R-DownlinkControl Information (R-DCI) format.

To achieve above another technical object, a relay node (RN) forreceiving signals in a wireless communication system includes a receiverfor receiving information about an aggregation level of a Relay-ControlChannel Element (R-CCE) from an eNode B, wherein the R-CCE is atransmission unit of a Relay-Physical Downlink Control Channel (R-PDCCH)including control information for the relay node, and a processor fordecoding the R-PDCCH in units of the R-CCE aggregation level based onthe received information about the R-CCE aggregation level.

The processor may control the receiver to receive a signal from theeNode B through a Relay-Physical Downlink Shared Channel (R-PDSCH)corresponding to the R-PDCCH based on control information of the decodedR-PDCCH.

The R-CCE aggregation level may be any one of 1, 2, 4, and 8. The R-CCEaggregation level may be applied to each of specific controlinformation. The R-CCE aggregation level may be transmitted through aspecific field of an R-Downlink Control Information (R-DCI) format.

Advantageous Effects

Using a signal reception method according to embodiments of the presentinvention, an RN can improve communication performance by successfullydecoding control information through a backhaul link from an eNB.

It will be appreciated by persons skilled in the art that that theeffects that can be achieved through the present invention are notlimited to what has been particularly described hereinabove and otheradvantages not mentioned above will be more clearly understood from thefollowing detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included as a part of the detaileddescription to provide a further understanding of the invention, provideembodiments of the invention and together with the description serve toexplain the principle of the invention. In the drawings,

FIG. 1 is a diagram schematically showing a network structure of anE-UMTS as an exemplary mobile communication system;

FIG. 2 is a block diagram showing the configuration of an eNB 205 and anRN 210 in a wireless communication system 200 according to the presentinvention;

FIG. 3 is a diagram showing the structure of a radio frame used in a3GPP LTE system which is an exemplary mobile communication system;

FIG. 4 is a diagram showing the structure of downlink and uplinksubframes of a 3GPP LTE system which is an exemplary mobilecommunication system;

FIG. 5 is a diagram showing a downlink time-frequency resource gridstructure used in the present invention;

FIG. 6 is a diagram showing the configuration of relay backhaul linksand relay access links in a wireless communication system;

FIG. 7 is a diagram showing an example of a resource area allocated byan eNB to an RN in a 3GPP LTE-A system which is an exemplary mobilecommunication system; and

FIG. 8 is a diagram showing an exemplary method for an eNB to allocatean RN zone in a specific backhaul subframe.

BEST MODE FOR CARRYING OUT THE INVENTION

Reference will now be made in detail to the exemplary embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. The detailed description, which will be given below withreference to the accompanying drawings, is intended to explain exemplaryembodiments of the present invention, rather than to show the onlyembodiments that can be implemented according to the invention. Thefollowing detailed description includes specific details in order toprovide a thorough understanding of the present invention. However, itwill be apparent to those skilled in the art that the present inventionmay be practiced without such specific details. For example, althoughthe following detailed description is given under the assumption of a3GPP LTE system as a mobile communication system, it is applicable toother arbitrary mobile communication systems except for matters that arespecific to the 3GPP LTE system.

In some instances, known structures and devices are omitted or are shownin block diagram, focusing on important features of the structures anddevices, so as not to obscure the concept of the present invention. Thesame reference numbers will be used throughout this specification torefer to the same parts.

The following description assumes that a User Equipment (UE) refers to amobile or fixed user equipment such as a Mobile Station (MS) or anAdvanced Mobile Station (AMS) and a Base Station (BS) refers to anarbitrary node of a network stage communicating with a UE, such as aNode B, an eNode B (eNB), or Access Point (AP). In addition, a RelayNode (RN) may be referred to as a Relay Station (RS) or a relay.

In a mobile communication system, a UE may receive information throughdownlink from an eNB, and the UE may transmit information throughuplink. Information transmitted and received by the UE includes data andvarious control information. A variety of physical channels are presentaccording to types or usages of information transmitted or received bythe UE.

FIG. 2 is a block diagram showing the configuration of an eNB 205 and anRN 210 in a wireless communication system 200 according to the presentinvention.

The wireless communication system 200 depicts one eNB 205 and one RN 210for sake of brevity. However, the wireless communication system 200 mayinclude more than one eNB and/or more than one RN.

Referring to FIG. 2, the eNB 205 may include a transmission (Tx) dataprocessor 215, a symbol modulator 220, a transmitter 225, atransmission/reception (Tx/Rx) antenna 230, a processor 280, a memory285, a receiver 290, a symbol demodulator 295, and a reception (Rx) dataprocessor 297. The RN 210 may include a Tx data processor 265, a symbolmodulator 270, a transmitter 275, a Tx/Rx antenna 235, a processor 255,a memory 260, a receiver 240, a symbol demodulator 245, and an Rx dataprocessor 250. Although one antenna 230 and one antenna 235 are depictedin the eNB 205 and the RN 210, respectively, each of the eNB 205 and theRN 210 includes a plurality of antennas. Accordingly, the eNB 205 andthe RN 210 according to the present invention support a Multiple InputMultiple Output (MIMO) system. The eNB 205 according to the presentinvention may support both a Single User-MIMO (SU-MIMO) scheme and aMulti User-MIMO (MU-MIMO) scheme.

In downlink, the Tx data processor 215 receives, formats, codes,interleaves, and modulates (or symbol maps) traffic data and providesmodulation symbols (“data symbols”). The symbol modulator 220 receivesand processes the data symbols and pilot symbols and provides a streamof symbols.

The symbol modulator 220 multiplexes the data and pilot symbols andtransmits the multiplexed symbols to the transmitter 225. Eachtransmission symbol may be a data symbol, a pilot symbol, or a signalvalue of zero. Pilot symbols may be sent continuously in each symbolperiod. Pilot symbols may be Frequency Division Multiplexed (FDM),Orthogonal Frequency Division Multiplexed (OFDM), Time DivisionMultiplexed (TDM), or Code Division Multiplexed (CDM) symbols.

The transmitter 225 receives and converts the stream of symbols into oneor more analog signals and further coordinates (e.g., amplifies,filters, and frequency up-converts) the analog signals to generate adownlink signal suitable for transmission over a radio channel. Thedownlink signal is then transmitted through the antenna 230 to the RN.

The configuration of the RN 210 is described. The antenna 235 of the RNreceives the downlink signal from the eNB 205 and provides the receivedsignal to the receiver 240. The receiver 240 coordinates (e.g., filters,amplifies, and frequency down-converts) the received signal anddigitizes the coordinated signal to obtain samples. The symboldemodulator 245 demodulates received pilot symbols and provides thedemodulated pilot symbols to the processor 255 for channel estimation.

The symbol demodulator 245 receives a frequency response estimate fordownlink from the processor 255, performs data demodulation uponreceived data symbols to obtain data symbol estimates (which areestimates of transmitted data symbols), and provides the data symbolestimates to the Rx data processor 250. The Rx data processor 250demodulates (e.g., symbol demaps), deinterleaves, and decodes the datasymbol estimates to recover the transmitted traffic data.

Processing by the symbol demodulator 245 and the Rx data processor 250is complementary to processing by the symbol modulator 220 and the Txdata processor 215, respectively, in the eNB 205.

In uplink, the Tx data processor 265 of the relay 210 processes trafficdata and provides data symbols. The symbol modulator 270 receives andmultiplexes the data symbols, performs modulation, and provides a streamof symbols to the transmitter 275. The transmitter 275 then receives andprocesses the stream of symbols to generate an uplink signal, which istransmitted through the antenna 235 to the eNB 205.

In the eNB 205, the uplink signal from the RN 210 is received throughthe antenna 230 and the receiver 290 processes the received uplinksignal to obtain samples. The symbol demodulator 295 then processes thesamples and provides received pilot symbols and data symbol estimatesfor uplink. The Rx data processor 297 processes the data symbolestimates to recover traffic data transmitted from the RN 210.

The processors 255 and 280 of the RN 210 and the eNB 205 direct (e.g.,control, coordinate, manage, etc.) operation at the RN 210 and the eNB205, respectively. The respective processors 255 and 280 may beconnected to the memories 260 and 285 that store program codes and data.The memories 260 and 285 are connected to the processor 280 to store anoperating system, applications, and general files.

The processors 255 and 280 may be referred to as controllers,microcontrollers, microprocessors, microcomputers, etc.

Meanwhile, the processors 255 and 280 may be implemented by hardware,firmware, software, or combinations thereof. When a signal receptionmethod of the RN according to embodiments of the present invention isachieved using hardware, Application Specific Integrated Circuits(ASICs), Digital Signal Processors (DSPs), Digital Signal ProcessingDevices (DSPDs), Programmable Logic Devices (PLDs), or FieldProgrammable Gate Arrays (FPGAs), which are configured to perform thepresent invention, may be included in the processors 255 and 280.

On the other hand, when the signal reception method of the RN accordingto embodiments of the present invention is achieved using firmware orsoftware, firmware or software may be configured to include a module, aprocedure, a function, etc. performing functions or operations of thepresent invention. The firmware or software configured to perform thepresent invention may be included in the processors 255 and 280 orstored in the memories 260 and 285 so as to be executed by theprocessors 255 and 280.

Layers of a radio interface between the RN 210 and eNB 205 and a radiocommunication system (network) may be divided into a first layer (L1), asecond layer (L2) and a third layer (L3), based on the three lowerlayers of an Open System interconnection (OSI) model widely known incommunication systems. A physical layer belonging to the first layerprovides information transfer services through a physical channel, ARadio Resource Control (RAC) layer belonging to the third layer providescontrol radio resources between a UE and the network. The RN 210 and theeNB 205 may exchange RRC messages with the radio communication networkthrough the RRC layer.

FIG. 3 is a diagram showing the structure of a radio frame used in a3GPP LTE system which is an exemplary mobile communication system.

Referring to FIG. 3, one radio frame has a length of 10 ms (327200T_(s)) and includes 10 equally-sized subframes. Each of the subframeshas a length of 1 ms and includes two slots. Each of the slots has alength of 0.5 ms (15360 T_(s)). In this case, T_(s) denotes samplingtime and is represented by T_(s)=1/(15 kHz×2048)=3.2552×10−8 (about 33ns). Each slot includes a plurality of OFDM symbols or SC-FDMA symbolsin a time domain and includes a plurality of resource blocks in afrequency domain.

In the LTE system, one resource block includes 12 subcarriers×7 (or 6)OFDM symbols or Single Carrier-Frequency Division Multiple Access(SC-FDMA) symbols. A Transmission Time Interval (TTI) which is a unittime for data transmission may be determined in units of one or moresubframes. The above-described structure of the radio frame is purelyexemplary and various modifications may be made in the number ofsubframes included in the radio frame, the number of slots included in asubframe, the number of OFDM or SC-FDMA symbols included in a slot.

FIG. 4 is a diagram showing the structure of downlink and uplinksubframes of a 3GPP LTE system which is an exemplary mobilecommunication system.

Referring to FIG. 4( a), one downlink subframe includes two slots in atime domain. A maximum of 3 front OFDM symbols of the first slot withinthe downlink subframe is a control region in which control channels areallocated, and the other OFDM symbols are a data region in which aPhysical Downlink Shared Channel (PDSCH) is allocated.

Downlink control channels used in the 3GPP LTE system include a PhysicalControl Format Indicator Channel (PCFICH), a Physical Downlink ControlChannel (PDCCH), a Physical Hybrid-ARQ Indicator Channel (PHICH), etc.The PCFICH, which is transmitted in the first OFDM symbol of a subframe,carries information about the number of OFDM symbols, (i.e. the size ofa control region), used for transmission of control channels within thesubframe. Control information transmitted through the PDCCH is referredto as Downlink Control Information (DCI). The DCI indicates uplinkresource allocation information, downlink resource allocationinformation, and an uplink transmit power control command for certain UEgroups. The PHICH carries Acknowledgement (ACK)/Negative-Acknowledgement(NACK) signals for uplink Hybrid Automatic Repeat Request (HARQ).Namely, the ACK/NACK signals for uplink data transmitted by a UE aretransmitted through the PHICH.

Now, a PDCCH, which is a downlink physical channel, is described.

An eNB may transmit, through the PDCCH, a PDSCH resource allocation andtransport format (this is called DL grant), an aggregate of transmitpower control commands for individual UEs within a certain UE group, andactivation of a Voice over Internet Protocol (VoIP). A plurality ofPDCCHs may be transmitted within a control region and a UE may monitorthe plurality of PDCCHs. The PDCCH consists of one or consecutiveControl Channel Element (CCE) aggregations. The PDCCH consisting of oneor a few consecutive CCE aggregations may be transmitted through thecontrol region after sub-block interleaving. A CCE is a logicalallocation unit used to provide a code rate according to the state of aradio channel to the PDCCH. The CCE corresponds to a plurality ofResource Element Groups (REGs). A format of the PDCCH and a possiblenumber of PDCCHs are determined according to a correlation between thenumber of CCEs and a code rate provided by the CCEs.

Control information transmitted through the PDCCH is referred to asDownlink Control Information (DCI). The following Table 1 shows DCIaccording to a DCI format.

TABLE 1 DCI format Description DCI format 0 Used for the scheduling ofPUSCH DCI format 1 Used for the scheduling of one PDSCH codeword DCIformat 1A Used for the compact scheduling of one PDSCH codeword andrandom access procedure initiated by a PDCCH order DCI format 1B Usedfor the compact scheduling of one PDSCH codeword with precodinginformation DCI format 1C Used for very compact scheduling of one PDSCHcodeword DCI format 1D Used for the compact scheduling of one PDSCHcodeword with precoding and power offset information DCI format 2 Usedfor scheduling PDSCH to UEs configured in closed-loop spatialmultiplexing mode DCI format 2A Used for scheduling PDSCH to UEsconfigured in open- loop spatial multiplexing mode DCI format 3 Used forthe transmission of TPC commands for PUCCH and PUSCH with 2-bit poweradjustments DCI format 3A Used for the transmission of TPC commands forPUCCH and PUSCH with single bit power adjustments

DCI format 0 indicates uplink resource allocation information. DCIformats 1 and 2 indicate downlink resource allocation information. DCIformats 3 and 3A indicate uplink Transmit Power Control (TPC) commandsfor certain UE groups.

A method for an eNB to map resources for PDCCH transmission in a 3GPPLTE system is described in brief.

Generally, the eNB may transmit scheduling allocation information andother control information through a PDCCH. A physical control channelmay be transmitted to one aggregate or a plurality of consecutive CCEs.That is, a unit for transmitting the PDCCH in the eNB is a CCE. One CCEincludes 9 REGs. The number of REGs which are not allocated to a PCFICHor PHICH is N_(REG). CCEs which are available in a system are from 0 toN_(CCE)−1 (where N_(CCE)=└N_(REG)/9┘). The PDCCH supports multipleformats as shown in the following Table 2. One PDCCH consisting of nconsecutive CCEs starts from a CCE performing i mode n=0 (where i is aCCE number). Multiple PDCCHs may be transmitted to one subframe.

TABLE 2 PDCCH Number of Number of resource Number of format CCEs elementgroups PDCCH bits 0 1 9 72 1 2 18 144 2 4 36 288 3 8 72 576

Referring to Table 2, the eNB may determine a PDCCH format depending onto how many regions control information is to be transmitted. A UE mayreduce overhead by reading control information in units of CCEs.Similarly, an RN may read control information in units of Relay-CCEs(R-CCEs). In an LTE-A system, the eNB may map Resource Elements (REs) inunits of R-CCEs to transmit a PDCCH for a certain RN, i.e. an R-PDCCH.

Referring to FIG. 4( b), an uplink subframe may be divided into acontrol region and a data region in a frequency domain. A PhysicalUplink Control Channel (PUCCH) is allocated to the control region todeliver uplink control information. A Physical Uplink Shared Channel(PUSCH) is allocated to the data region to deliver user data. Tomaintain a single carrier characteristic, one UE does not transmit thePUCCH and the PUSCH simultaneously. A PUCCH for one UE may be allocatedas a Resource Block (RB) pair in one subframe. RBs belonging to the RBpair occupy different subcarriers in two slots. The RB pair allocated tothe PUCCH is frequency-hopped at a slot boundary.

FIG. 5 is a diagram showing a downlink time-frequency resource gridstructure used in the present invention.

A downlink signal transmitted in each slot uses a resource gridstructure including N_(RB) ^(DL)×N_(SC) ^(RB) subcarriers and N_(symb)^(DL) OFDM symbols, wherein N_(RB) ^(DL) represents the number of RBs indownlink, N_(SC) ^(RB) represents the number of subcarriers constitutingone RB, and N_(symb) ^(DL) represents the number of OFDM symbols in onedownlink slot. The size of N_(RB) ^(DL) varies according to a downlinktransmission bandwidth configured within a cell and should satisfyN_(RB) ^(min,DL)≦N_(RB) ^(DL)≦N_(RB) ^(max,DL), wherein NR_(RB)^(min,DL) denotes the smallest downlink bandwidth supported by awireless communication system and N_(RB) ^(max,RB) denotes the greatestdownlink bandwidth supported by a wireless communication system. N_(RB)^(min,DL) may be 6 and N_(RB) ^(max,RB) may be 110. However, the presentinvention is not limited thereto. The number of OFDM symbols included inone slot may vary according to the length of a Cyclic Prefix (CP) andthe spacing of subcarriers. In the case of MIMO transmission, oneresource grid per antenna port may be defined.

Each element in the resource grid for each antenna port is called an REand is uniquely identified by an index pair (k, l) in a slot, wherein kis a frequency-domain index having any one value of 0 to N_(RB)^(DL)N_(SC) ^(RB)−1 and l is a time-domain index having any one value of0 to N_(symb) ^(DL)−1.

The RB shown in FIG. 5 is used to describe a mapping relationshipbetween any physical channel and REs. The RB may be divided into aPhysical Resource Block (PRB) and a Virtual Resource Block (VRB). OnePRB is defined as N_(symb) ^(DL) consecutive OFDM symbols in a timedomain and N_(SC) ^(RB) consecutive subcarriers in a frequency domain,wherein N_(DL) ^(symb) and N_(SC) ^(RB) may be predetermined. Forexample, N_(DL) ^(symb) and N_(SC) ^(RB) may be given as shown in thefollowing Table 3. Accordingly, one PRB includes N_(symb) ^(DL)×N_(SC)^(RB) REs. Although one PRB may correspond to one slot in a time domainand to 180 kHz in a frequency domain, the present invention is notlimited thereto.

TABLE 3 Configuration N_(SC) ^(RB) N_(symb) ^(DL) Normal cyclic Δf = 15kHz 12 7 prefix Extended cyclic Δf = 15 kHz 6 prefix Δf = 7.5 kHz 24 3

The PRB has a value ranging from 0 to N_(RB) ^(DL)−1. A relationshipbetween a PRB number n_(PRB) in a frequency domain and a RE (k,l) in oneslot satisfies

$n_{PRB} = {\left\lfloor \frac{k}{N_{SC}^{RB}} \right\rfloor.}$

The size of the VRB is the same as the size of the PRB. The VRB may bedivided into Localized VRB (LVRB) and a Distributed VRB (DVRB). Withrespect to each type of VRB, one pair of VRBs in two slots within onesubframe is allocated together with a single VRB number n_(VRB).

The size of the VRB may be the same as the size of the PRB. Two types ofVRBs are defined as Localized VRB (LVRB) and a Distributed VRB (DVRB).With respect to each type of VRB, a pair of VRBs is allocated over twoslots of one subframe with a single VRB index (hereinafter, may bereferred to as a VRB number). In other words, any one index ranging from0 to N_(RB) ^(DL)−1 is allocated to N_(RB) ^(DL) VRBs belonging to afirst slot of two slots constituting one subframe and similarly any oneindex ranging from 0 to N_(RB) ^(DL)−1 is allocated to N_(RB) ^(DL) VRBsbelonging to a second slot of two slots constituting one subframe.

The above-described radio frame structure, downlink and uplinksubframes, and downlink time-frequency resource grid structure shown inFIG. 3 to FIG. 5 may be applied to an eNB-RN structure.

An R-PDCCH used in the present invention refers to a backhaul physicaldownlink control channel for relay transmission from the eNB to the RN.An R-PUCCH is used to refer to a backhaul physical uplink controlchannel for relay transmission from the RN to the eNB. An R-PDSCH isused to refer to a backhaul downlink physical data shared channel forrelay transmission. An R-PUSCH is used to refer to a backhaul uplinkphysical data shared channel for relay transmission.

Although the RN used in the present invention is described as ahalf-duplex RN in which simultaneous bidirectional transmission andreception through the same band is not possible, the RN is notnecessarily limited to a half-duplex scheme.

FIG. 6 is a diagram showing the configuration of relay backhaul linksand relay access links in a wireless communication system.

Referring to FIG. 6, while an LTE-A system introduces a role offorwarding a link between an eNB and a UE to an RN, two types of linkshaving different attributes are applied to uplink and downlink carrierfrequency bands. A link part connected between the eNB and the RN isdefined as a backhaul link. Transmission through a Frequency DivisionDuplexing (FDD) or time Division Duplexing (TDD) scheme using downlinkresources may be expressed as a backhaul downlink, and transmissionthrough an FDD or TDD scheme using uplink resources may be expressed asa backhaul uplink.

The RN may receive information from the eNB through a relay backhauldownlink and may transmit information to the eNB through a relaybackhaul uplink. The RN may transmit information to a UE through a relayaccess downlink and may receive information from the UE through a relayaccess uplink.

The eNB is necessary to additionally configure a new physical controlchannel for the RN while maintaining compatibility with LTE release-8.Here, the new physical control channel for the RN is referred to as anR-PDCCH and a data channel for the RN is referred to as an R-PDSCH. AnRN zone may include the R-PDCCH and the R-PDSCH.

When the eNB allocates resources for the R-PDCCH in the LTE-A system,reliability, scheduling flexibility, and decoding latency areconsidered. In terms of reliability, it is possible to obtain ascheduling gain or diversity gain for the R-PDCCH. In addition, it isalso possible to cause the RN to blindly decode an allocated R-PDCCH orto allocate a specific R-PDCCH to each RN. In terms of schedulingflexibility, the eNB may dynamically allocate resources in an RN zone.In terms of decoding latency, the eNB desirably reduces decoding latencyby allocating resources using a TDM scheme rather than an FDM schemebetween the R-PDCCH and the R-PDSCH. Although the present inventionapplies the TDM scheme as a multiplexing scheme between the R-PDCCH andthe R-PDSCH, it is apparent that the same method may be applied evenwhen the FDM scheme is applied.

In an LTE system, the RN cannot receive a PDCCH from the eNB. Althoughit is possible to receive the PDCCH when a subframe of the RN is set tobe advanced by 2 or 3 OFDM symbols compared to a subframe of the eNB, itis difficult to perform cooperative transmission between the eNB and theRN. Due to backhaul link quality and a semi-static characteristic oftraffic load, dynamic resource allocation as in communication betweenthe eNB and the UE may be unnecessary. Namely, the RN may be configuredto transmit signals through a fixed Modulation and Coding Scheme (MCS)using a fixed band according to a subframe pattern for prescribedbackhaul communication. Moreover, the eNB may perform distributedresource allocation or localized resource allocation for the RN.

FIG. 7 is a diagram showing an example of a resource area allocated byan eNB to an RN in a 3GPP LTE-A system which is an exemplary mobilecommunication system.

FIG. 7( a) illustrates a method in which an eNB multiplexes a newphysical control channel 710 for an RN, (i.e. an R-PDCCH), and a datachannel 720 for an RN, (i.e. an R-PDSCH or PDSCH for RNs) through a TimeDivision Multiplexing (TDM) scheme. Upon multiplexing the R-PDCCH andR-PDSCH, the eNB may configure a subframe allocated for correspondingbackhaul transmission as a Multicast Broadcast Single Frequency Network(MBSFN) in order to maintain compatibility with LTE release-8 and mayallocate the new physical control channel 710 and data channel 720 forthe RN through the TDM scheme to an MBSFN data region (a part except fora control channel of the MBSFN subframe).

In a subframe allocated for backhaul transmission illustrated in FIG. 7(b), a specific band is allocated as a physical control channel 730 forthe RN. Namely, the physical control channel 730 for the RN and a datachannel 740 may be multiplexed within a PDSCH region of thecorresponding subframe through an FDM scheme and then allocated. Even inthis case, the eNB allocates resources to each RN in consideration oftraffic load as if the eNB allocates resources to a UE, and the eNBinforms the RN of information about resource allocation through thephysical control channel 730. The eNB may allocate an additionalphysical control channel 730 for the RN while maintaining compatibilitywith LTE release-8.

In a subframe allocated for backhaul transmission illustrated in FIG. 7(c), the eNB allocates a specific band as a physical control channel 750for the RN. The eNB may multiplex the physical control channel 730 forthe RN and a data channel 760 within a corresponding band through TDM.Even in this case, the eNB allocates resources to each RN inconsideration of traffic load as if the eNB allocates resources to a UE,and the eNB informs the RN of information about resource allocationthrough the physical control channel 750. The eNB may allocate anadditional physical control channel 750 for the RN while maintainingcompatibility with LTE release-8.

As described earlier, a newly allocated physical control channel for theRN by the eNB is referred to as an R-PDCCH. Each RN may perform blindsearch for resources allocated dynamically for downlink backhaultransmission through an RN identifier (ID). Namely, each RN may detectan R-PDCCH directing the RN by performing, through the RN ID, blinddecoding of a time/frequency domain in which the dynamically allocatedR-PDCCH is transmitted and may obtain DL grant, UL grant, and controlinformation (e.g. ACK/NACK feedback information) through the detectedR-PDCCH. The eNB may inform the RN of information about an RB to besearched by the RN through higher layer signaling. The RN may performblind search (or decoding) based on the received information about theRB to be searched. In this case, higher layer signaling may betransmitted from the eNB to the RN as a semi-static signal.

An R-PDSCH, which is a downlink backhaul data channel transmitted by theeNB to each RN, may be multiplexed for allocation with the R-PDCCHthrough TDM in the backhaul subframe as illustrated in FIG. 7( a),through FDM in the backhaul subframe as illustrated in FIG. 7( b), orthrough TDM or a hybrid of TDM and FDM as in FIG. 7( c).

FIG. 8 is a diagram showing an exemplary method for an eNB to allocatean RN zone in a specific backhaul subframe.

Referring to FIG. 8, an RN zone 810 includes an R-PDCCH 811 and anR-PDSCH 812 in a specific backhaul subframe shown in FIG. 8 and may bepreconfigured for both channels. The R-PDCCH 811 and the R-PDSCH 812 maybe multiplexed in a time domain within one RN zone 810. The eNB 205 mayobtain a diversity gain using a method of mapping an LTE CCE to REs overthe R-PDCCH 811. The processor 255 of the RN 210 (e.g. the RN 1, RN 2,or RN 3 shown in FIG. 7) may detect a region of the R-PDCCH 811 byperforming blind search within the previously configured RN zone 810.

As illustrated in FIG. 8, the R-PDSCH 812 transmitted to RNs isscheduled within the zone 810. The size of the RN zone 810 is notdynamically adjusted according to the amount of traffic for RNs. PDSCHs813 and 814 transmitted to LTE macro UEs are not scheduled in the RNzone 810.

The eNB may RN-specifically determine a search space to be performedblind search by each RN. The eNB may transmit the determined RN-specificsearch space to each RN through higher layer signaling. Alternatively,the search space in which each RN performs blind search may becell-specifically determined, and the eNB may broadcast informationabout the search space (e.g. information about an RB to be searched) toall RNs through cell-specific system information or may transmit theinformation about the search space to each RN through higher layersignaling. The RN-specific search space or cell-specific search spacesignaled to each RN may include a subset of RBs. In this case, the eNBmay explicitly signal indexes of OFDM symbols in which the R-PDCCH istransmitted to each RN. Alternatively, indexes of OFDM symbols or slotsin which the R-PDCCH is transmitted may be implicitly fixed so that theRN may be aware of the indexes.

In an LTE-A system, REs may be mapped in units of Relay-Control ChannelElements (R-CCEs) to transmit the R-PDCCH for an arbitrary RN.Hereinafter, a method for mapping resources to REs when the eNBdynamically allocates resources for R-PDCCH transmission will bedescribed.

<Resource Mapping Method 1 when Resources are Dynamically Allocated>

As a first method, a method may be considered for fixing OFDM symbolsfor an R-PDCCH at OFDM symbols of indexes 3 to 6 in a time domain of aspecific backhaul subframe and varying the number of RBs in a frequencydomain.

When a logical basic unit of R-PDCCH transmission for an arbitrary RN byan eNB is defined as an R-CCE, a modulation scheme for R-CCEtransmission is determined according to link quality between the eNB andthe RN. If the modulation scheme is determined, the number of necessaryREs for one R-CCE transmission and indexes of OFDM symbols in whichR-PDCCH transmission is performed are determined. One or more OFDMsymbols in which R-PDCCH transmission is performed may be implicitlyfixed or explicitly signaled to the RN by the eNB. In this case, uponexplicitly signaling the OFDM symbols to the RN, the eNB may transmitthe OFDM symbols through higher layer signaling to each RN as anRN-specific value, may broadcast the OFDM symbols to all RNs in the formof cell-specific system information as a cell-specific value, or maytransmit the OFDM symbols to each RN through higher layer signaling.

Mapping of one R-CCE to REs is basically performed in units of RBs or RBpairs. Namely, although the eNB may explicitly signal the size of oneR-CCE (i.e. the number of RBs or RB pairs) to each RN, the size of oneR-CCE may be implicitly determined according to the modulation schemeand used OFDM symbols so that the RN is aware of the size of one R-CCE.The RN may perform blind decoding based on an R-CCE size and an R-CCEaggregation level. Namely, if the size of one R-CCE is 4 RB pairs, blindsearch may be performed in units of 4 consecutive RB pairs.

Multiple search spaces may be configured per R-CCE aggregation. If thenumber of RB pairs necessary to transmit one R-CCE is determined, asearch space is configured according to the R-CCE aggregation level. TheRN performs blind search for each search space using RB granularityaccording to the R-CCE aggregation level.

A variable R-CCE size structure rather than an R-CCE aggregationstructure based on a fixed R-CCE size may be applied to each RNaccording to link quality for each RN. The R-CCE size may be differentaccording to an RN-specific search space for an arbitrary RN or acell-specific search space. For example, in the case of an RN-specificsearch space 1 for an RN 1, the R-CCE size may be 2 RB pairs and in thecase of an RN-specific search space 2, the R-CCE size may be 3 RB pairs.Each RN may perform blind search based on a corresponding R-CCE size.The eNB may use a fixed modulation order for R-CCE transmission at onevalue.

An embodiment of the above-described method for fixing an R-PDCCH at oneor more OFDM symbols (e.g. OFDM symbols of indexes 3 to 6) in a timedomain and varying the number of RBs in a frequency domain will now bedescribed.

First, it is assumed that 16 Quadrature Amplitude Modulation (QAM) isapplied to the RN 1 as a modulation scheme for R-PDCCH transmission andQuadrature Phase Shift Keying (QPSK) is applied to the RN 2 as amodulation scheme for R-PDCCH transmission. However, the R-PDCCHmodulation scheme applied to each RN is only exemplary and themodulation scheme may be fixed so that the same modulation scheme isimplicitly applied to all RNs. It is also assumed that a backhaulsubframe uses a normal CP and the R-PDCCH is transmitted to both the RN1 and the RN 2 through OFDM symbols of indexes 3, 4, 5, and 6. It isalso assumed that a Channel State Indicator-Reference Signal (CSI-RS) isnot transmitted in the OFDM symbols of indexes 3, 4, 5, and 6.

Under the above assumption, the number of REs which can be used forR-PDCCH transmission through one RB pair is 44, and the RN 1 and RN 2can transmit 176 bits and 88 bits, respectively.

In the case of the RN 1, if the R-PDCCH is set to have the R-CCE size of2 RB pairs, a search space 1 (e.g. RB pair indexes 0 to 15) isconfigured to perform blind search based on an R-CCE aggregation level1, a search space 2 (e.g. RB pair indexes 16 to 31) is configured toperform blind search based on an R-CCE aggregation level 2, and a searchspace 3 (e.g. RB pair indexes 32 to 63) is configured to perform blindsearch based on an R-CCE aggregation level 4, then the RN 1 performsblind decoding a total of 16 times, that is, 16/2=8 times in the searchspace 1, 16/4=4 times in the search space 2, and 32/8=4 times in thesearch space 3.

In the case of the RN 2, if the R-PDCCH is set to have the R-CCE size of4 RB pairs, a search space 1 (e.g. RB pair indexes 16 to 31) isconfigured to perform blind search based on an R-CCE aggregation level1, a search space 2 (e.g. RB pair indexes 32 to 63) is configured toperform blind search based on an R-CCE aggregation level 2, and a searchspace 3 (e.g. RB pair indexes 64 to 95) is configured to perform blindsearch based on an R-CCE aggregation level 4, then the RN 2 performsblind decoding of 16/4=4 times in the search space 1, 32/8=4 times inthe search space 2, and 32/16=2 times in the search space 3.

<Method for Supporting Blind Search in an RN According to ResourceMapping for R-PDCCH Transmission>

1. Explicit Signaling Method

In mapping resources according to the above-described method 1 fordynamically allocating resources, a method for an eNB to support blindsearch for an R-PDCCH in an RN is described. Namely, a method for an eNBto support blind search (or decoding) of an RN is described whenconsidering the method for fixing OFDM symbols for the R-PDCCH at OFDMsymbol indexes 3 to 6 (e.g. OFDM symbols of indexes 3 to 6 of the firstslot of a backhaul subframe) in a time domain and varying the number ofRBs in a frequency domain.

As a method for an eNB to support blind search in an RN according to theresource mapping method for R-PDCCH transmission, ‘R-CCE aggregationlevel’ signaling is discussed. A method for signaling the R-CCEaggregation level broadly includes a method for the eNB to explicitlysignal the R-CCE aggregation level to the RN and a method for causingthe RN to implicitly be aware of the R-CCE aggregation level withoutexplicit signaling.

Conventionally, in downlink, the eNB has signaled the size of a PDCCH toa UE etc. through a PCFICH so that the UE etc. can be aware of a startpoint of a time domain (or symbol region) of a PDSCH. However, a startpoint of an R-PDSCH may vary according to whether an R-PDCCH has beentransmitted per PRB and according to the aggregation level of anR-PDCCH, as opposed to the case of the PDSCH. Accordingly, the eNB mayexplicitly signal information indicating an R-CCE aggregation level tothe RN for the purpose of successful decoding of control information ofthe RN.

When the eNB transmits the R-PDCCH for a specific RN (e.g. RN 1) througharbitrary PRBs (or RB pairs), it may be assumed that the remaining REsexcept for REs used for R-PDCCH transmission within the correspondingPRBs are used for R-PDSCH transmission for the same RN (e.g. RN 1).Namely, it may be assumed that the eNB does not simultaneously transmitthe R-PDCCH and the R-PDSCH for different RNs within the same PRB. Undersuch assumption, an example of an R-DCI format of the R-PDCCHtransmitted by the eNB to the RN is shown in the following Table 4.

TABLE 4 R-DCI format Description R-DCI format 0 R-PUSCH allocation R-DCIformat 1 and 2 series R-PDSCH allocation R-DCI format 3 series TransmitPower Control (TPC)

In addition to the R-DCI format proposed in Table 4, an information areaindicating an R-CCE aggregation level for corresponding R-PDCCHtransmission in all R-DCI formats which can be newly definedbackhaul-link specifically may be defined. For example, when an R-CCEaggregation level for one R-PDCCH transmission supports 4 aggregationlevels of 1, 2, 4, and 8, R-CCE aggregation level indication fieldsindicating R-CCE aggregation levels for the respective R-DCI formats(e.g. R-DCI format 0, 1, 2, and 3 series) may be defined. The number ofbits constituting the R-CCE aggregation level indication field may bedifferently defined according to the number of R-CCE aggregation levelssupported for R-PDCCH transmission. For example, if the number ofsupported R-CCE aggregation levels is N, the number of bits constitutingthe R-CCE aggregation level indication field may be defined as floor(log₂N). Here, a floor function refers to a function which outputs aminimum value among integers greater than or equal to a designatednumber.

Unlike the above description, the eNB may multiplex, for transmission,an R-PDCCH for a specific RN and an R-PDSCH for another RN through a TDMscheme within the same PRB. In this case, in a structure of an R-DCIformat 1 series defined for R-PDSCH allocation, an information areaindicating whether the R-PDCCH has been transmitted within acorresponding RB and indicating an R-CCE aggregation level of theR-PDCCH may be defined together with RB allocation information, duringR-PDSCH resource allocation.

As described above, the eNB may explicitly signal the R-CCE aggregationlevel for R-PDCCH transmission to each RN. For example, let us assumethat the eNB transmits an R-CCE, which is a transmission unit of anR-PDCCH including control information for a specific RN (RN 1), at anaggregation level 2. In other words, it is assumed that the eNBtransmits specific control information (e.g. DL grant) for the RN 1through 2 RB pairs. If the eNB does not inform the RN 1 of the R-CCEaggregation level, the RN 1 performs blind decoding only for the firstof the 2 RB pairs. In this way, the RN 1 performs blind decoding onlyfor an R-PDCCH transmitted through the first slot of the first RB pairto receive an R-PDSCH transmitted through the second slot of the firstRB pair.

As the RN 1 is not aware of the R-CCE aggregation level information eventhough the eNB actually transmits control information through the firstslot of the second RB pair, the RN 1 determines that the R-PDSCH istransmitted even in the first slot of the second RB pair, therebycausing decoding failure. Accordingly, it is necessary for the eNB toexplicitly inform the RN 1 of the R-CCE aggregation level information sothat the RN 1 can accurately receive control information. The RN 1decodes the R-PDCCH region in units of R-CCE aggregation levels based onthe R-CCE aggregation level information. The RN 1 can receive signalsfrom the eNB through the R-PDSCH region corresponding to the R-PDCCHregion which has successfully performed decoding.

The RN can discern the R-CCE aggregation level through such explicitsignaling and can also implicitly discern the R-CCE aggregation levelfor R-PDCCH transmission.

2. Implicit Signaling Method

As an example, the eNB may enable the RN to discern an R-CCE aggregationlevel by using different scrambling sequences with respect to R-CCEaggregation levels of an R-PDCCH for a specific RN. In this case, if theeNB transmits the R-PDCCH using different scrambling sequences withrespect to R-CCE aggregation levels, the RN can be implicitly aware ofthe R-CCE aggregation level by discerning a scrambling sequence appliedto the transmitted R-PDCCH. Thus, the eNB uses different scramblingsequences to inform the RN of the R-CCE aggregation level during R-PDCCHtransmission. A method for differently applying scrambling sequences toR-CCE aggregation levels may apply different scrambling sequences byvarying an initial value of a currently defined scrambling sequence ormay vary the definition of the scrambling sequences.

As another example, the eNB may enable the RN to be aware of the R-CCEaggregation level applied to the R-PDCCH by differently applying CyclicRedundancy Check (CRC) masking of the R-PDCCH. The RN may require an RNRadio Network Temporary Identifier (RNTI) for blind search in theR-PDCCH. The eNB may transmit the RN RNTI by masking it to CRC and, inthis case, the eNB may differently CRC mask the RN RNTI according to theR-CCE aggregation level. Through CRC masking, a UE can determine whetherthe UE can decode a corresponding codeword and CRC masking is definedbased on an RNTI value.

As another example, the eNB may enable the RN to be aware of the R-CCEaggregation level applied to the R-PDCCH by differently applyingpermutation upon mapping of a CCE to REs in the R-PDCCH. Bits of theR-PDCCH are aggregated such that 4 bits are grouped into a pair(quadruplet) and passes through a subblock interleaver. Next, if thepermutation or subblock interleaver is differently applied according tothe R-CCE aggregation level, the RN may implicitly discern the R-CCEaggregation level applied to the R-PDCCH.

As another example, the eNB may enable the RN to be aware of the R-CCEaggregation level applied to the R-PDCCH by changing a mapping order ofsymbols or REs within an REG of the R-PDCCH. When the bits of theR-PDCCH are actually mapped to the REG as a quadruplet, the eNB maychange the mapping order according to the R-CCE aggregation level. Forexample, let us assume that one REG includes 4 REs over 4 subcarrierswith respect to one symbol index. The eNB may enable the RN to be awareof the R-CCE aggregation level applied to the R-PDCCH by changing anorder of mapping R-PDCCH bits with respect to REs or symbols within anREG according to the R-CCE aggregation level and then transmitting theR-PDCCH. In this way, the RN can easily discern the R-CCE aggregationlevel through a simple method of changing a mapping order of REs ormodulated symbols within an REG.

As another example, the eNB may enable the RN to be aware of the R-CCEaggregation level applied to the R-PDCCH by changing a mapping order toan REG unit within an R-CCE of the R-PDCCH. During mapping to REGswithin an R-CCE in units of R-CCE aggregation levels (9 REGs per CCE aredefined in an LTE system), the eNB may change a mapping order to theREGs with respect to each R-CCE aggregation level to transmit theR-PDCCH so that the RN can be implicitly aware of the R-CCE aggregationlevel applied to the R-PDCCH.

As another example, the eNB may enable the RN to be aware of the R-CCEaggregation level applied to the R-PDCCH by changing a mapping orderbetween R-CCEs of the R-PDCCH. In the LTE system, symbols are mapped toone CCE and to another CCE. However, since a different number of R-CCEsis used according to the R-CCE aggregation level, a mapping orderconfiguration may be changed such that symbols are sequentially mappedonly to partial resources within a corresponding R-CCE according toR-CCE indexes with respect to a used number of R-CCEs (in this case,although a mapping unit is determined based on an REG, it may bedetermined based on a subcarrier) and are sequentially mapped even tothe other REG indexes within the R-CCE. Namely, symbols may first bemapped to the first REG of each R-CCE and then may be mapped to thesecond REG.

Thus, the eNB may enable the RN to be aware of the R-CCE aggregationlevel applied to the R-PDCCH using an explicit or implicit method withrespect to an R-CCE aggregation level. The RN performs blind search (ordecoding) in unit of R-CCE aggregation levels by explicitly receivingsignaling for the R-CCE aggregation level from the eNB or implicitlyrecognizing the R-CCE aggregation level. The RN may receive controlinformation by performing the blind search (or decoding) in units ofR-CCE aggregation levels and may receive data from the eNB based on thecontrol information.

<Resource Mapping Method 2 when Resources are Dynamically Allocated>

Another resource mapping method for R-PDCCH transmission and a blindsearch method in an RN according to the resource mapping method aredescribed. As a second method for mapping an R-CCE to REs to transmit anR-PDCCH for an arbitrary RN, a method for fixing the number of RBs of afrequency domain and varying the number of OFDM symbols of a time domainis considered.

Like the above description of the resource mapping method 1 whenresources are dynamically allocated, if a logical basic unit of R-PDCCHtransmission for an arbitrary RN is defined as an R-CCE, a modulationscheme for R-CCE transmission is determined according to link qualitybetween an eNB and an RN. If the modulation scheme is determined, thenumber of necessary REs for unit R-CCE transmission and the number of RBpairs in which R-PDCCH transmission is performed are determined.

An R-CCE aggregation level is determined by the number of one or moreOFDM symbols used for R-CCE transmission within an RB pair in whichR-CCE, a basic logical unit of R-PDCCH transmission, is transmitted.Namely, if the R-CCE aggregation level is 1, one OFDM symbol is used forR-CCE transmission, and if the R-CCE aggregation level is 2, 2 OFDMsymbols are used. If the R-CCE aggregation level is 3, 3 OFDM symbolsare used for R-CCE transmission.

A plurality of search spaces per R-CCE aggregation level may beconfigured. If the number of VRBs necessary for transmitting one R-CCEis determined, a search space is configured according to the R-CCEaggregation level. Each search space may have the same RB position. AnRN may perform blind search of each search space based on the number ofOFDM symbols at the same RB granularity according to the R-CCEaggregation level.

Namely, in the case of a search space 1, the RN may perform blind searchbased on one OFDM symbol, and in the case of a search space 2, the RNmay perform blind search based on two OFDM symbols.

<Resource Mapping Method 3 when Resources are Dynamically Allocated>

Another resource mapping method for R-PDCCH transmission and a blindsearch method in an RN according to the resource mapping method aredescribed. As a third method for mapping an R-CCE to REs to transmit anR-PDCCH for an arbitrary RN, a method for fixing the number of RB pairsof a frequency domain and the number of OFDM symbols of a time domainand varying a modulation scheme may be considered.

A modulation scheme used for R-PDCCH transmission may vary according toa search space. Namely, an eNB may transmit an R-PDCCH based on a QPSKscheme in the case of a search space 1 for an arbitrary RN 1 and maytransmit the R-PDCCH based on a 16 QAM scheme in the case of a searchspace 2.

The above-described three resource mapping methods when resources aredynamically allocated to transmit the R-PDCCH may be applied in a hybridform.

<Resource Mapping Method 4 when Resources are Dynamically Allocated>

The R-PDCCH may use a DCI format which is different from that used by alegacy UE or an LTE-A UE. An example of an R-PDCCH format transmitted byan eNB to an RN may be indicated as shown in the following Table 5.

TABLE 5 R-PDCCH format Description R-PDCCH format 0 UL grant for R-PUSCHtransmission R-PDCCH format 1 and 2 DL grant for R-PUSCH transmissionseries R-PDCCH format 3 series Transmit Power Control Command (TPC)

The case where the eNB transmits the R-PDCCH for an RN 1 is described.Upon transmitting a plurality of R-PDCCHs for an RN 1, the eNB maytransmit the R-PDCCHs by multiplexing them through a TDM scheme by usingconsecutive OFDM symbols in the same RB or RB pair according to apredefined rule. For example, if the first R-PDCCH is transmitted withina given RB pair through 4 OFDM symbols from OFDM symbol indexes 3 to 6of the first slot, the second R-PDCCH may be transmitted through thesecond slot of the corresponding RB pair. Here, the plurality ofR-PDCCHs may be R-PDCCHs having different formats. For example, formatsof a plurality of R-PDCCHs may include R-PDCCH formats 1 and 2 fortransmitting DL grant, which is control information necessary for theeNB to transmit data to the RN, and an R-PDCCH format 0 for transmittingUL grant, which is necessary for the RN to transmit data to the eNB. Fortransmission, the DL grant may be allocated to the first slot in aspecific RB pair and the UL grant may be allocated to the second slotwhich consecutively follows the first slot. Especially, according to apredefined rule, the DL grant may be transmitted through 4 consecutiveOFDM symbols of OFDM symbol indexes 3 to 6 in the first slot and the ULgrant may be transmitted through 7 consecutive OFDM symbols of OFDMsymbol indexes 7 to 13 in the second slot.

When the eNB transmits a plurality of R-PDCCHs to a specific RN, thecorresponding RN can be aware of an RB position, in which anotherR-PDCCH directing the RN is transmitted, through blind search withrespect to one R-PDCCH. Namely, the R-PDCCH directing the correspondingRN is multiplexed using a TDM scheme through contiguous OFDM symbols inthe same frequency position and then transmitted.

Upon detecting one R-PDCCH, the RN performs blind decoding of subsequentOFDM symbols once more. If the RN successfully receives an additionalPDCCH of another format through blind decoding of the subsequent OFDMsymbols, the RN may perform blind decoding of the next subsequent OFDMsymbols once more. The RN performs blind decoding until the RN fails todecode an additional R-PDCCH in corresponding RB pairs.

For example, let us assume that an RN 1 performs R-PDCCH blind search ofOFDM symbols of indexes 3 to 6, an R-CCE size of 2 RB pairs for onesearch space (RB or RB pair indexes 0 to 31) is used, both DL grant andUL grant are transmitted, and the RN 1 succeeds in detecting the DLgrant in an RB pair of an index is 24 through blind search of OFDMsymbols only of indexes 3 to 6 in RB pairs of indexes 0 to 31. Thensince the RN 1 has successfully detected the DL grant in the RB pair ofan index 24, the RN 1 further performs blind decoding of OFDM symbols ofindexes 7 to 13, which is another RB, in the RB pair of the index 24,thereby confirming whether an additional R-PDCCH is present. In thiscase, after succeeding in detecting UL grant in OFDM symbols of indexes7 to 13 in the RB pair of the index 24, the RN 1 performs blind decodingin the next RB pair (i.e. an RB pair of an index 25) and may confirmthat there is no additional R-PDCCH.

It has been described that a plurality of R-PDCCHs are allocated using aTDM scheme in consecutive RBs. Similarly, a method for fixing theposition of R-PDCCHs by allocating a plurality of R-PDCCHs in the formof FDM through consecutive RBs may be considered.

The above-described embodiments are combinations of elements andfeatures of the present invention in a predetermined type. Each of theelements or features may be considered selective unless otherwisementioned. Each element or feature may be practiced without beingcombined with other elements or features. Further, an embodiment of thepresent invention may be constructed by combining parts of the elementsand/or features. Operation orders described in embodiments of thepresent invention may be rearranged. Some constructions of any oneembodiment may be included in another embodiment and may be replacedwith corresponding constructions of another embodiment. In the appendedclaims, it will be apparent that claims which are not explicitlydependent on each other can be combined to provide an embodiment or newclaims can be added through amendment after this application is filed.

Those skilled in the art will appreciate that the present invention maybe embodied in other specific ways than those set forth herein withoutdeparting from the spirit and essential characteristics of the presentinvention. The above embodiments are therefore to be construed in allaspects as illustrative and not restrictive. The scope of the inventionshould be determined by the appended claims and their legal equivalentsand all changes coming within the meaning and equivalency range of theappended claims are intended to be embraced therein.

INDUSTRIAL APPLICABILITY

The RN for receiving signals from the eNB and the signal receptionmethod of the RN is applicable to wireless communication systems such as3GPP LTE, LTE-A, and IEEE 802 systems.

What is claimed is:
 1. A method of transmitting a relay-physicaldownlink control channel (R-PDCCH) by a base station in a wirelesscommunication system, the method comprising: transmitting firstinformation indicating a pattern of subframes configured for the basestation to a relay node (RN) transmission and second informationindicating a set of resources blocks; mapping the R-PDCCH to aRN-specific search space of a subframe; and transmitting the subframecarrying the R-PDCCH according to the pattern of subframes, wherein theRN-specific search space of the subframe is located in the set ofresource blocks indicated by the second information, and wherein theR-PDCCH is mapped in a first slot of the received subframe if theR-PDCCH corresponds to a downlink assignment for the RN, and the R-PDCCHis mapped in a second slot of the received subframe if the R-PDCCHcorresponds to a uplink grant for the RN.
 2. The method of claim 1,further comprising: transmitting third information used for determininga position of a starting symbol of a physical downlink shared channel(PDSCH) for the RN.
 3. The method of claim 2, wherein the position ofthe starting symbol of the PDSCH for the RN varies in a time domainaccording to the third information and the third information isexplicitly signaled by the base station, and a position of a startingsymbol of the R-PDCCH is implicitly prescribed.
 4. The method of claim1, wherein a position of a starting symbol of the R-PDCCH within in thefirst slot of the subframe is fixed in a time domain.
 5. The method ofclaim 1, wherein symbol indexes of the R-PDCCH within the first slot ofthe subframe are fixed as ‘3’ to ‘6’.
 6. The method of claim 1, whereina length of the R-PDCCH within the first slot of the subframecorresponding to 4 symbols.
 7. The method of claim 1, wherein thesubframe contains a PDCCH for at least one user equipment (UE) and aphysical downlink shared channel (PDSCH) for the RN, and the PDCCH forthe UE is mapped on a control region of the subframe, and both of theR-PDCCH and the PDSCH for the RN are mapped on a data region of thesubframe.
 8. A base station comprising: a transmitter configured totransmit first information indicating a pattern of subframes configuredfor the base station to a relay node (RN) transmission and secondinformation indicating a set of resources blocks, and to transmit asubframe capable of carrying a relay-physical downlink control channel(R-PDCCH) according to the pattern of subframes, and a processorconfigured to map the R-PDCCH to a RN-specific search space of thesubframe, wherein the RN-specific search space of the subframe islocated in the set of resource blocks indicated by the secondinformation, and wherein the R-PDCCH is mapped in a first slot of thereceived subframe if the R-PDCCH corresponds to a downlink assignmentfor the RN, and the R-PDCCH is mapped in a second slot of the receivedsubframe if the R-PDCCH corresponds to a uplink grant for the RN.
 9. Thebase station of claim 1, wherein the transmitter transmits thirdinformation used for determining a position of a starting symbol of aphysical downlink shared channel (PDSCH) for the RN.
 10. The basestation of claim 9, wherein the position of the starting symbol of thePDSCH for the RN varies in a time domain according to the thirdinformation and the third information is explicitly signaled by the basestation, and a position of a starting symbol of the R-PDCCH isimplicitly prescribed.
 11. The base station of claim 8, wherein aposition of a starting symbol of the R-PDCCH within in the first slot ofthe subframe is fixed in a time domain.
 12. The base station of claim 8,wherein symbol indexes of the R-PDCCH within the first slot of thesubframe are fixed as ‘3’ to ‘6’.
 13. The base station of claim 8,wherein a length of the R-PDCCH within the first slot of the subframecorresponding to 4 symbols.
 14. The base station of claim 8, wherein thesubframe contains a PDCCH for at least one user equipment (UE) and aphysical downlink shared channel (PDSCH) for the RN, and the PDCCH forthe UE is mapped on a control region of the subframe, and both of theR-PDCCH and the PDSCH for the RN are mapped on a data region of thesubframe.
 15. A method of receiving a relay-physical downlink controlchannel (R-PDCCH) by a relay node (RN) in a wireless communicationsystem, the method comprising: receiving first information indicating apattern of subframes configured for a base station to the RNtransmission and second information indicating a set of resourcesblocks; receiving a subframe capable of carrying the R-PDCCH accordingto the pattern of subframes; and searching a RN-specific search space ofthe received subframe to detect the R-PDCCH based on a control channelelement (CCE) aggregation level, wherein the RN-specific search space ofthe received subframe is located in the set of resource blocks indicatedby the second information, and wherein the R-PDCCH is in a first slot ofthe received subframe if the R-PDCCH corresponds to a downlinkassignment for the RN, and the R-PDCCH is in a second slot of thereceived subframe if the R-PDCCH corresponds to a uplink grant for theRN.
 16. The method of claim 15, wherein a position of a starting symbolof the R-PDCCH within in the first slot of the subframe is fixed in atime domain.
 17. The method of claim 15, wherein symbol indexes of theR-PDCCH within the first slot of the subframe are fixed as ‘3’ to ‘6’.18. The method of claim 15, wherein a length of the R-PDCCH within thefirst slot of the subframe corresponding to 4 symbols.
 19. A relay node(RN) comprising: a receiver configured to receive first informationindicating a pattern of subframes configured for a base station to theRN transmission and second information indicating a set of resourcesblocks and to receive a subframe capable of carrying a relay-physicaldownlink control channel (R-PDCCH) according to the pattern ofsubframes; and a processor configured to control the receiver and tosearch a RN-specific search space of the received subframe to detect theR-PDCCH based on a control channel element (CCE) aggregation level,wherein the RN-specific search space of the received subframe is locatedin the set of resource blocks indicated by the second information, andwherein the R-PDCCH is in a first slot of the received subframe if theR-PDCCH corresponds to a downlink assignment for the RN, and the R-PDCCHis in a second slot of the received subframe if the R-PDCCH correspondsto a uplink grant for the RN.